This invention relates to prelubricated aluminum strip material and the production of shaped articles, e.g. heat exchanger fins, utilizing such aluminum strip material.
Conventionally, heat exchangers have been constructed with a very narrow fin spacing in order to provide a design in which the surface areas of the heat radiating part and the cooling part are as large as possible. The condensation of water droplets on the fins tends to interfere with air flow and, accordingly, it has been necessary to provide hydrophilic coatings on the fins which make possible very rapid removal of any water that condenses on the fins. One known method of rendering the fins hydrophilic is the Boehmiting process.
The heat exchanger fins are formed from a finstock. This is typically an aluminum material which is formed into the fins by passing through a finpress die.
At present, most finstock is flooded with lubricating oil prior to feeding into a finpress. As a result, the environment of the finpress is oily and most unpleasant and, moreover, the fins must be degreased after forming. The most commonly used organic solvent for this purpose is trichloroethylene. The use of organic solvents, such as trichloroethylene, for degreasing poses various problems, such as: (1) health hazards, (2) odour, (3) fire hazards and (4) the problem of handling and disposing of oil/solvent mixtures.
Many of the above problems can be eliminated by the use of prelubricated finstock, since the finstock user then no longer needs to apply any lubricating oil prior to forming. Within the past few years, the use of "evaporative" lubricating oils has been promoted as a means of eliminating the degreasing procedure. These evaporative oils are very dilute (approximately 10%) solutions of lubricating oil in mineral spirits. After forming, the mineral spirits evaporate from the fins, thereby eliminating the need for degreasing. However, residual oil remains on the fin surfaces. While this residual oil does not present any problems in handling of the fins, when heat exchangers, such as evaporators, are constructed using these fins, the residual oil can interfere with hydrophilic treating processes such as the Boehmiting process.